JP2006526362A - Method and apparatus for performing soft handoff in a wireless communication system - Google Patents

Abstract

A mobile station typically determines whether to delete a communication link and / or base transceiver station (BTS) based on the performance of the associated forward link. In order to avoid deleting a communication link (220) that has a weak forward link (222) but a strong reverse link (224), the reverse link is still Provided is a communication system for determining whether it is good or not. In one embodiment, the communication system may include a quality measure associated with the reverse link and one or more other reverse links (234) in reverse link and soft handoff mode. To determine whether the reverse link (224) is still good. In other embodiments, the communication system determines whether the reverse link (224) is still good by comparing the threshold with a quality measure associated with the reverse link.

Description

  The present invention relates generally to wireless communication systems, and more particularly to soft handoff in wireless communication systems.

Wireless communication systems are well known, many types including land mobile radio, cellular wireless telephones (including analog cellular, digital cellular, personal communication systems (PCS) and broadband digital cellular systems), and others The communication system type.
In a cellular radiotelephone communication system, for example, typically a number of communication cells are connected to one or more base station controllers (BCS) or central base station controller (CBCS) to form a base station subsystem (BSS). It consists of one or more base transceiver stations (BTS). The BSC or CBSC is connected to the mobile switching center (MSC), and the mobile switching center (MSC)
Provides connectivity between the BSS and an external network such as a public switched telephone network (PTSN) and interconnection to other BSSs. Each BTS is located in the coverage area served by the BTS via a communication resource that includes a forward link for transmitting signals to the MS and a reverse link for receiving signals from the MS. Providing communication services to the mobile station (MS).

  Fundamental to a wireless communication system is the ability to maintain an established communication connection while the MS moves within and between coverage areas. In order to maintain established communication connections, soft handoff techniques have been developed for code division multiple access (CDMA) communication systems, whereby the MS performs simultaneous active communication with multiple BTSs. Each BTS that is in active communication with the MS is a member of the MS's active set and sends carrier traffic to the MS and receives carrier traffic from the MS. As the MS moves through the communication system, BTSs are added to or removed from the active set of MSs to ensure that the MS is always in communication with at least one BTS.

For example, FIG. 1 is a block diagram of a prior art CDMA wireless communication system 100. The communication system 100 includes a BSS 104, and the BSS 104 includes a number of BTSs 106 to 108 each connected to the CBSC 110. The BSS 104 is connected to the MSC 114 and the MSC 114 is connected to the external network 116 and provides a communication link between the external network or other BSS and the BSS 104. Further, the communication system 100 includes an MS 102 that is in active communication with the BTSs 106 and 107 simultaneously. That is, MS 102 is in soft handoff with each of BTSs 106 and 107, and BTS 106 and BTS 107 are each a member of the active set of MSs 102. As a member of the active set of MS 102, each BTS of BTSs 106 and 107 simultaneously maintains a respective wireless communication link 120, 130 with the MS. Each communication link 120, 130 includes a respective forward link 122, 132 for communicating signals to the MS 102, and a respective reverse link 124, 134 for receiving signals from the MS.

Each BTS 106, 107 in the active set of MS 102 communicates the same carrier traffic to the MS and receives the same carrier traffic from the MS. By providing multiple BTSs that simultaneously transmit the same signal to the MS 102 and receive the same signal from the MS 102, the communication system 100 allows the MS to receive an acceptable quality signal from the BSS 104, and the BSS Increase the likelihood of receiving an acceptable quality signal from the MS. For example, if each BTS of BTSs 106 and 107 receives the same frame from MS 102, the BTS determines whether the received frame is acceptable or incorrect, and whether the frame and the frame are acceptable, That is, it forwards to the CBSC 110 an attached index that indicates whether it is good or wrong, ie, erased. Then, the CBSC 110, specifically, the selection / distribution unit (SDU) 112 included in the CBSC selects one version of the received frame from the versions received from the BTSs 106 and 107, and sends the selected version to the MSC 114. Forward.

The signal strength of the pilot signal received by the MS 102 from the BTS 108 over the forward link 142 associated with the BTS 108 as the MS 102 moves toward the coverage area or sector associated with the BTS 108 is the communication that the MS 102 can survive. Increase until the pilot signal from the BTS 108 is identified as a link. Further, as the MS 102 moves away from the coverage area associated with the BTS 106, i.e., the sector, the signal strength of the pilot signal received by the MS 102 from the BTS 106 via the forward link 122 indicates that the communication link 120 is no longer viable. It can be degraded to the point where the MS 102 determines that it is not a link. Then, the MS 102 uses the forward link 142 and the reverse link 144 as active communication links for transmitting and receiving data to and from the MS 102 so that the communication system 100 adds the BTS 108 to the active set of MSs. Including to establish a communication link 140 associated with the BTS 108 and to remove the BTS 106 from the active set, ie
Requests that communication link 120 be terminated. Typically, the request to delete the BTS is communicated by the MS 102 via a pilot strength measurement message (PSMM). Upon receipt of the PSMM message, the BSS 104 deletes the BTS 106 from the active set of the MS 102 and terminates, ie deletes the communication link 120 between the MS 102 and the BTS 106.
The decision to add or remove communication links 120, 130, 140 and corresponding BTSs 106, 107, 108 from the active set is received by the MS, such as MS 102, via the forward link measurement, ie, the corresponding forward link. Based on measurement of the signal strength of the pilot signal. That is, when making an add and / or delete decision, the communication system 100 determines that the performance of the forward links 122, 132, 142 is substantially the same as the performance of the corresponding reverse links 124, 134, 144. Assume. However, if there is an imbalance between the performance of the forward links, such as forward links 122, 132, 142, etc., and the performance of the corresponding reverse links, ie, the respective reverse links 124, 134, and 144 Problems arise. For example, a sector served by a BTS may experience interference specific to the reverse link, or the propagation path and fading associated with each of the forward and reverse links in the sector may be May differ due to frequency band separation with reverse link. As a result, a communication link with a strong reverse link may be deleted due to a weak forward link. The reverse link of the deleted communication link, such as reverse link 124 of communication link 120, is the only good reverse link among the multiple reverse links utilized by the MS, such as reverse links 124 and 134. If the communication link is deleted, the call may be deleted.

  Therefore, as part of the soft handoff, it is necessary to ensure that the communication system can confirm that the good reverse link is not about to be deleted, thereby ensuring that the communication link is not terminated, i.e. not deleted. .

As part of soft handoff, a need for a method and apparatus that guarantees until a communication system can confirm that a communication link is not terminated, i.e., is not being deleted, thereby ensuring that a good reverse link is not being deleted. To address this, a communication system is provided that determines whether the reverse link is still good before deciding to delete the communication link. In one embodiment, the communication system includes a quality measure associated with the reverse link;
And determining whether the reverse link is still good based on the quality measure (s) associated with the reverse link and one or more other reverse links that are in soft handoff mode. In other embodiments, the communication system determines whether the reverse link is still good by comparing a quality measure associated with the reverse link to a threshold. In addition, the communication system allows communication with MSs that degrade to an unacceptable level as a result of maintaining a communication link with little margin by allowing the system infrastructure to re-determine whether to delete the communication link. To prevent.

  In general, embodiments of the present invention cover a method for performing soft handoff in a wireless communication system. The method includes receiving a plurality of frames from the mobile station via each of the first reverse link and the second reverse link, and based on the plurality of frames received via the first reverse link. Determining a first reverse link quality measure and determining a second reverse link quality measure based on a plurality of frames received via the second reverse link. Further, the method includes receiving a request to delete a communication link including the first reverse link, comparing the first reverse link quality measure and the second reverse link quality measure, and obtaining a comparison value. Generating and determining whether to delete the communication link based on the comparison value in response to receiving the request.

  Other embodiments of the present invention cover a method for performing soft handoff in a wireless communication system. The method includes receiving a plurality of frames from a mobile station via a reverse link and determining a reverse link quality measure based on the plurality of frames. Further, the method includes receiving a request to delete a communication link that includes a reverse link, generating a comparison value by comparing the reverse link quality measure with a threshold, and receiving the request. Responsive to the step of determining whether to delete the communication link based on the comparison value.

  Yet another embodiment of the present invention covers an apparatus for performing soft handoff in a wireless infrastructure. The apparatus receives a plurality of frames from the mobile station via each of the first reverse link and the second reverse link, and based on the plurality of frames received via the first reverse link, Determining a first reverse link quality measure, determining a second reverse link quality measure based on a plurality of frames received over the second reverse link, and determining the first reverse link quality measure and the second reverse link A processor is included that compares the link quality measures to generate a comparison value. Further, the processor receives a request to delete a communication link including the first reverse link, and determines whether to delete the communication link based on the comparison value in response to receiving the request.

  Yet another embodiment of the present invention covers an apparatus for performing soft handoff in a wireless infrastructure. The apparatus includes a processor connected to one or more memory devices. The processor receives a plurality of frames from a mobile station via a reverse link, stores a quality index associated with each frame of the plurality of frames in one or more memory devices, and based on the stored quality index, A reverse link quality measure is determined, and the reverse link quality measure is compared with a threshold value to generate a comparison value. Further, the processor receives a request to delete a communication link that includes a reverse link, and determines whether to delete the communication link based on the comparison value in response to receiving the request.

The present invention will be described in more detail with reference to FIGS. FIG. 2 is a block diagram of a CDMA wireless communication system 200 according to an embodiment of the present invention. Similar to communication system 100, communication system 200 includes a base including a number of transmit / receive base stations (BTS) 206-208 each connected to a controller 210, such as a base station controller (BSC) or a central base station controller (CBSC). A station subsystem (BSS) 204 is included. The BSS 204 is connected to a mobile switching center (MSC) 216 and the MSC 216 is connected to an external network 218 and provides a communication link between the external network, ie, another BSS (not shown), and the BSS 204. To do. BS
S204 and MSC 216 may be collectively referred to as the infrastructure of communication system 200.

The controller 210, preferably the selection and distribution unit (SDU) 212 included in the controller, includes one or more microprocessors, microcontrollers, digital signal processors (DSPs), combinations thereof or known to those skilled in the art. A processor 213 such as another device is included. In addition, controller 210 may include random access memory (RAM), dynamic random access memory (DRAM), and / or read only memory (ROM).
Alternatively, one or more memory devices 214 associated with the processor 213 are included, such as data that can be executed by the processor and their equivalents storing programs.

Furthermore, the communication system 200 includes a mobile station (MS) 202 that is in active communication with the BTSs 206 207 at the same time. That is, the MS 202 is in a “soft handoff” mode with multiple BTSs 206, 207, and each BTS of the multiple BTSs 206, 207 is a member of the MS 202 active set. As part of the active set of MS 202, each BTS of a number of BTSs 206, 207
Each wireless communication link 220, 230 with the MS is maintained simultaneously. Each communication link 220, 230 includes a respective forward link 222, 232 to convey a signal to the MS 202 and includes a respective reverse link 224, 234 to receive a signal from the MS.

Preferably, communication system 200 is a code division multiple access (CDMA) communication system, where forward links 222, 232, and 242 and reverse links 224, 234, and 244 each include an access channel. A number of communication channels are included, such as a control channel, a paging channel, and a traffic channel. Each communication channel of the reverse link 224, 232, 242 or the forward link 224, 234, 244 includes an orthogonal code such as a Walsh code that can be transmitted in the same frequency bandwidth as the other channels of the link. However, the communication system 200 is not limited to this, but is a global system for a mobile communication (GSM) communication system, a time division multiple access (TDMA) communication system, a frequency division multiple access (FDMA) communication system, or Those skilled in the art will recognize that they can operate based on any wireless telecommunications system, such as an orthogonal frequency division multiple access (OFDM) communication system.

When the communication system 200 is operating in soft handoff mode, the first plurality of frames transmitted by the MS 202 is transmitted over each reverse link 224, 234 to each of a number of BTSs 206, 207 in the active set of MSs. Received by the BTS. Then, each BTS of the multiple BTSs 206 and 207 transfers a plurality of frames received by the BTS to the controller 210, and further transfers one or more quality indexes indicating the quality of the received plurality of frames. .

The one or more quality indices transferred by each BTS 206, 207 are based on a frame quality measure that may be determined for each frame or for multiple frames. For example, the frame quality measure may be a frame error rate (FER) determined for multiple frames, or a bit error rate (BER), signal-to-noise ratio (SNR), signal strength, carrier-to-interference ratio ( CIR) or Eb / Io ratio (energy per bit / interference power density (per hertz)) determined for one or more of the frames. Those skilled in the art will recognize that many quality measures are known and can be used herein without departing from the spirit and scope of the present invention.

The quality index may include a frame quality measure and may be an index representing the frame quality measure. For example, the BTS may determine whether the received frame is acceptable or incorrect for each frame and based on the frame quality measure. The BTS embeds a quality index in the header of the frame, which indicates whether the frame is acceptable, i.e. good, or wrong, i.e. erased. The BTS then forwards the frame and the embedded quality index to the controller 210.

When the controller 210 receives a plurality of frames and associated one or more quality indexes from each of a number of BTSs 206, 207, the controller may be associated with the BTS supplying the plurality of frames and / or of the plurality of frames. One or more quality indexes are stored in one or more memory devices 214 in connection with a reverse link or communication link via reception. When the same frame is received from each of the multiple BTSs 206, 207, the controller 210 then selects one frame from the same frames received from each BTS, and selects the selected frame as the MSC 216.
Forward to. Unless otherwise specified herein, controller 210 may be used herein.
All functions performed by are preferably performed by the SDU 212, in particular by the processor 213.

As the MS 202 moves within the communication system 200, the MS goes to a coverage area associated with a BTS that is not in the MS's active set, such as BTS 208, ie, toward a sector, and is associated with a BTS that is in the active set, such as BTS 206 It can be away from the coverage area, i.e. the sector. MS202
As the MS moves to the BTS 208 side, the signal strength of the pilot signal received by the MS 202 via the forward link 242 associated with the BTS 208 increases until the MS 202 identifies the pilot signal from the BTS 208 as a viable communication link. . Further, as the MS 102 moves away from the BTS 206, the signal strength of the pilot signal received by the MS 202 from the BTS 206 via the forward link 222 degrades to the point that the MS 202 determines that the communication link 220 is no longer a viable communication link. To do. In that regard, communication system 200 adds BTS 208 and communication link 240 (ie, to the active set of MS 202) and deletes BTS 206 and communication link 220 (ie, from the active set of MS 202). Determine if a soft handoff should be performed.

FIG. 3 is a logical flow diagram 300 of steps performed by the communication system 200 in determining whether to perform a soft handoff, according to an embodiment of the present invention. The logic flow diagram 300 begins when the MS 202 moves to the communication system 100, where the communication system adds a BTS 208 to the active set of MSs and includes a forward link 242 and a reverse link 244.
The communication link 240 related to S208 is established as an active communication link, and a request to transmit / receive data to / from the MS 102 is received from the MS. Further, the MS 202 is connected to the communication system 100.
Moving on to the communication system, the communication system deletes the first BTS 206, 207 of the multiple BTSs 206, 207 in the active set of the MS 202, and the first communication link associated with the first BTS, ie, the communication link 220. A request to end, that is, delete, is received from the MS (302). Preferably, the request to delete BTS 206 and / or communication link 220 is communicated by MS 202 using a pilot strength measurement message (PSMM) in which a request to delete BTS and / or communication link is embedded.

As part of a soft handoff, to ensure that the communication system 220 can confirm that the communication link 220 is not terminated, i.e. not deleted, the communication system 200 is also not trying to delete the good reverse link 224 The communication system 200 first determines whether the reverse link is a good link before determining whether the corresponding communication link should be deleted. In one embodiment of the invention, to determine whether reverse link 224 is a good link, controller 210 determines a first reverse link, ie, a first reverse link quality measure for reverse link 224. (304), but this first reverse link is associated with the BTS 206 and communication link 220 under the deletion target. Further, the controller 210 determines a second reverse link quality measure for the second reverse link (306), which is a number of BTSs 206 in the active set of the MS 202, such as the reverse link 234, Related to other BTSs at 207.

Controller 210 then compares 308 the first reverse link quality measure and the second reverse link quality measure to generate a comparison value. Based on this comparison value and in response to a delete request,
The controller 210 determines whether to delete the first reverse link, i.e., reverse link 224, and the associated first communication link, i.e., communication link 220, and the associated first BTS,
That is, it is determined whether the BTS 206 should be deleted from the active set of the MS 202 (310). And
The logic flow diagram 300 ends.

The controller 210 is based on a plurality of frames received from the MS 202 via the first reverse link, i.e., the reverse link 224, and in particular, is associated with a plurality of frames received via the first reverse link. A first reverse link quality measure is determined based on one or more quality indices of one. The controller 210 is based on a plurality of frames received from the MS 202 via the second reverse link, ie, the reverse link 234, and in particular, a second associated with the plurality of frames received via the second link. A second reverse link quality measure is determined based on the one or more quality indexes.

For example, in one embodiment of the present invention, in determining each of the first and second reverse link quality measures, the controller 210 is received from one or more memory devices 214 via the corresponding reverse link. In addition, one or more quality indexes stored for a predetermined number of frames received prior to receiving the delete request are retrieved. Preferably, the controller retrieves the quality index associated with the 120 previous frame. However, those skilled in the art will recognize that the number of frames used is not critical to the present invention and is up to the designer of the system 200. In other embodiments of the present invention, the controller 210 may retrieve one or more quality indexes stored for frames received over the reverse link during a predetermined period prior to the delete request. A predetermined number of frames or a predetermined period may be maintained in one or more memory devices 214.

If each of the first and second one or more quality indices includes an indication of whether the received frame is a good frame or an erasure frame, the controller 210 may select the first and second Each of the first and second reverse link quality measures may be determined by determining an erasure frame quantity based on the one or more quality indices. For example, in step 304, the controller 210 may determine a first reverse link quality measure by determining a first erasure frame quantity received over the first reverse link, ie, reverse link 224. . Similarly, in step 306, the controller 210 determines a second reverse link quality measure by determining a second erasure frame quantity received over the second reverse link, ie, reverse link 234. obtain. As another example, in step 304, the controller 210 determines the first reverse link quality measure by determining a good first frame quantity received over the first reverse link, ie, reverse link 224. Can be determined. Similarly, at step 306, the controller 210 determines a second reverse link quality measure by determining a good second quantity frame received over the second reverse link, ie, reverse link 234. Can do.

If the first reverse link quality measure and the second reverse link quality measure include the first frame quantity and the second frame quantity, respectively, step 308 compares the first quantity and the second quantity to generate a comparison value. May include the step of: Then, the comparison value obtained as a result is a first quantity corresponding to the first reverse link, that is, the reverse link 224, and a second quantity corresponding to the second reverse link, that is, the reverse link 234. May include differences between. The step of determining whether to delete the communication link 220 and / or BTS 206, ie, step 310, may include the following steps. If the determined difference exceeds the difference threshold stored in one or more memory devices 214, the controller 210 determines that the first reverse link, i.e., reverse link 224, is no longer a good link. to decide. Controller 210 then decides to accept the delete request, that is, delete communication link 220 and delete BTS 206 from the active set of MS 202. If the determined difference does not exceed the difference threshold, the controller 210 determines that the first reverse link, i.e., reverse link 224, is still a good link, and further ignores the delete request, i.e. The reverse link 224, the communication link 220, and the BTS 206 are determined not to be deleted.

Although communication system 200 is shown as including only two BTSs in the active set of MS 202, those skilled in the art will readily apply the principles of the invention described herein to a larger active set. Recognize that you get. For example, if more than two reverse links are associated with a BTS in the active set, the controller 210 may determine the first reverse link quality measure, i.e.
The reverse link quality measure determined for the reverse link under deletion may be compared with the optimal reverse link quality measure determined for other reverse links associated with the BTS in the active set. As another example, more than two reverse links may result in BT in the active set.
If so, the controller 210 may compare the first reverse link quality measure with an average value of the reverse link quality measure determined for the other reverse links. Those skilled in the art will use other algorithms herein that may be used herein without departing from the spirit and scope of the present invention, and the reverse link quality measure determined for the reverse link that is being deleted. It should be appreciated that the reverse link quality measure determined for the BTS of one or more other reverse links in the active set may be compared.

By determining whether the reverse link 224 associated with the communication link 220 or BTS 206 to be deleted is still good, the communication system 200 can request that the communication link with the strong reverse link be based on a weak forward link. To ensure that it is not deleted in response to. As a result, it is possible to delete a call if the reverse link of the deleted communication link, such as reverse link 224 of communication link 220, is the only good reverse link of many reverse links in soft handoff Is minimized. In order to avoid good reverse link deletion, the controller 210 is in a quality measure associated with the reverse link 224 of the communication link 220 to be deleted and is in soft handoff mode with the reverse link 224, i.e. BTS 206. Same MS202
Compare the quality measure (s) associated with one or more other reverse links 234 associated with other BTSs 207 in the active set.

Based on the comparison value of the reverse link quality measure, the controller 210 determines whether the reverse link 224 is still a good link, or whether the reverse link 224 is associated with all the reverse links 224, 234 associated with the MS. It is possible to determine whether the communication link 220 and / or BTS 206 to be deleted is to be deleted.

If the communication system 200 decides not to delete the first communication link 220 and / or the first BTS 206 based on the comparison value between the first reverse link quality measure and the second reverse link quality measure, the controller 210 One BTS 206 and associated communication link 220 may be continuously considered as candidates for deletion and other deletion decisions may be initiated. FIG. 4 is a block diagram of a communication system in accordance with various embodiments of the present invention when first determining not to delete communication link 220 and / or first BTS 206 and then making subsequent decisions as to whether to delete that link or BTS. 4 is a logic flow diagram 400 of the steps performed by 200. Once the logic flow diagram 400 begins, the controller 210 determines 402 to not delete the first communication link, ie, the communication link 220, and / or the first BTS, ie, the BTS 206. Following the decision not to delete the communication link and / or BTS, each BTS of the multiple BTSs 206, 207 in the active set of MS 202 receives a second plurality of frames from the MS, and receives the received second plurality of frames, Transfer to controller 210 along with one or more quality indices associated with the transferred second plurality of frames.

Upon receiving a second plurality of frames and associated one or more quality indexes from each of the BTSs 206 and 207 (404), the controller 210 receives each received in association with the corresponding BTS, reverse link, or communication link. The quality index is stored in one or more memory devices 214 (406). When the first time period expires without receiving a delete request from the MS 202, the controller 210 is based on the second plurality of frames received over the first reverse link, and preferably the first reverse direction. Based on the one or more quality indices stored for the second plurality of frames received over the link, a third reverse link quality measure for the first reverse link, i.e., reverse link 224, is determined (408). ). Further, the controller 210 is stored based on the second plurality of frames received via the second reverse link, and preferably for the second plurality of frames received via the second reverse link. Based on the one or more quality indexes, a fourth reverse link quality measure for the second reverse link, i.e., reverse link 234, is determined (410).

Controller 210 then compares the third reverse link quality measure with the fourth reverse link quality measure to generate a second comparison value (412). Based on the second comparison value, the controller 210 determines whether to terminate or delete the first communication link, i.e., the communication link 220, and / or
A determination is made as to whether the first BTS, ie, BTS 206, should be deleted from the active set of MS 202 (414). The logic flow diagram 400 then ends.

As noted above, in some embodiments of the present invention, the reverse link quality measure includes a determined amount, such as the number of frames received in an acceptable state or the number of frames received in error. obtain. If the third reverse link quality measure includes the third quantity and the fourth reverse link quality measure includes the fourth quantity, step 412 compares the third quantity with the fourth quantity and generates a quantity difference. May include the step of: And in such a case, step 414 may include determining whether to delete communication link 220 and / or BTS 206 based on the comparison value between the quantity difference and the difference threshold.

In another embodiment of the invention shown in FIG. 4, instead of the controller 210 deleting instead of making a subsequent determination of whether to delete the communication link 220 and / or BTS 206 without receiving a subsequent deletion request, Once determined, if communication link 220 and BTS 206 are to be considered as candidates for deletion continually, controller 210 may instruct MS 202 to communicate a deletion / non-deletion message at the expiration of the second time period (416). The delete / non-delete message indicates any desire of the MS to delete the communication link 220 and / or BTS 206 or not. Preferably,
Controller 210 instructs the MS to send a delete / non-delete message by communicating a pilot measurement request command to MS 202.

Upon receipt of this indication, the MS 202 moves to the controller 210, which deletes / shows the desire to delete the communication link 220 and / or BTS 206 or not.
A non-deletion message is received from the MS (418). Preferably, the deletion / non-deletion message includes a PSMM message in which the MS has embedded an indication of whether to delete or not delete the communication link and / or BTS. Deletion / non-deletion messages may be communicated to communication link 220 and / or BTS 206
, Controller 210 determines a third reverse link quality measure for first reverse link 224 and further determines a fourth reverse link quality measure for second reverse link 234 (420 However, the determination of these measures is described in detail above with respect to steps 408 and 410. The logic flow diagram 400 then proceeds to step 412 where the controller 210 performs a third operation.
The reverse link quality measure and the fourth reverse link quality measure are compared to generate a comparison value, and based on the comparison value, it is determined whether the communication link 220 and / or BTS 206 should be deleted (414). The logic flow diagram 400 then ends.

Controller 210 determines again whether communication link 220 and / or BTS 206 should be deleted.
By doing so, the communication system 200 maintains a communication link 220 that may be marginal, and as a result, the risks associated with degrading communication with the MS to an unacceptable level. Provide a proactive infrastructure to minimize. After receiving a request to delete communication link 220 and / or BTS 206, and in response to the delete request, deciding not to delete communication link or BTS, communication system 200, in particular controller 210, may delete another Whether the communication link or BTS should be deleted may be redetermined either by itself without receiving a request or by instructing the MS 202 to send a delete / non-delete message. In re-determining whether to delete communication link 220 and / or BTS 206, controller 210 follows the decision not to delete, and based on the frame received from MS 202 via reverse link 224, the associated reverse link. 224 determines if it is still a good link.

In other embodiments of the present invention, the determination of whether to perform a soft handoff is made with respect to only one reverse link associated with the communication link 220 or BTS 206 being deleted, ie, the reverse link with respect to the reverse link 224. It can be simplified by involving the determination of a quality measure. FIG. 5 is a logical flow diagram 500 of the steps performed by the communication system 200 in determining whether to perform a soft handoff, according to such an embodiment of the present invention. When logic flow diagram 500 begins, communication system 200 may request that MS 202 remove BTS 206 from the active set and / or terminate communication link 220 and associated reverse link 224, ie, delete. (502). Controller 210 then determines a first reverse link quality measure for the reverse link to be deleted, ie, reverse link 224 (504). The controller 210 compares the first reverse link quality measure and the quality measure threshold stored in the one or more memory devices 214 to generate a first comparison value (506). Then, based on the first comparison value, the controller 210 determines the communication link 220 and / or the BTS 206.
It is determined whether or not to be deleted (508). Then the logic flow 500 ends.

As described above with respect to logic flow diagram 300, controller 210 may store a predetermined number of frames received over reverse link 224 prior to receiving a delete request or during a predetermined period prior to a delete request. A first reverse link quality measure may be determined based on one or more quality indices stored for frames received over the reverse link. If the stored one or more quality indices include an indication of whether the frame is a good frame or an erasure frame, step 504 may determine whether the number of erasure frames received over reverse link 224 or Determining a first reverse link quality measure by controller 210 by determining a frame quantity based on a stored quality index, such as a good frame quantity, may be included. Step 506 may then include the step of comparing the determined frame quantity with the threshold stored in the one or more memory devices 214 by the controller 210 to generate a first comparison value.

Then, step 508 may include the following steps. Based on the first comparison value, if the number of frames is inferior compared to the threshold, the controller 210 determines that the reverse link, i.e., reverse link 224 is no longer a good link, and further communicates. It may be determined that link 220 and / or BTS 206 should be deleted. However, if the frame quantity is comparable to the threshold, the controller 210 determines that the reverse link, i.e., the reverse link 224 is still a good link, and further includes the communication links 220 and / or Alternatively, it may be decided not to delete the BTS 206.

For example, the controller 210 determines the number of erase frames received over the reverse link 224 at step 504, and further, at step 506, the determined number of erase frames is determined by the erase frame threshold. If so, the controller 210 may determine that the reverse link 224 is no longer a good link. However, if the determined number of erase frames does not exceed the erase frame threshold, the controller 210 may determine that the reverse link 224 remains a good link. As another example, the controller 210 determines in step 504 the number of good frames received over the reverse link 224, and further in step 506 the determined number of good frames is If it is determined that the good frame threshold is exceeded, the controller 210 may determine that the reverse link 224 is still a good link. However, if the determined quantity of good frames does not exceed the good frame threshold, the controller 210
May determine that reverse link 224 is no longer a good link.

In yet another embodiment of the present invention, if it is determined at step 510 that communication link 220 and / or BTS 206 are not to be deleted, controller 210 continually considers communication link 220 and BTS 206 as deletion candidates, and other deletion decisions. Can start. FIG. 6 is a logic flow diagram 600 of handoff performance by a communication system in accordance with various other embodiments of the present invention. When logic flow diagram 600 begins, controller 210 determines not to delete communication link 220 and / or BTS 206 (602). Following the decision not to delete, the BTS being deleted, ie BT
S206 receives a second plurality of frames from the MS via the reverse link being deleted, i.e., reverse link 224, and receives the second plurality received along with one or more associated quality indexes. Transfer the frame to the controller 210.

Upon receiving a second plurality of frames and associated one or more quality indexes from BTS 206 (604), controller 210 may receive one or more received in association with the corresponding BTS, reverse link, or communication link. The quality index is stored in one or more memory devices 214 (606). When the third time period expires without receiving a delete request from the MS 202, the controller 210 is based on the second plurality of frames received via the reverse link, and preferably via the reverse link. A second reverse link quality measure for the reverse link 224 is determined based on the one or more stored quality indices for the received second plurality of frames (608). And controller 210
Compares the second reverse link quality measure and the quality measure threshold to generate a second comparison value (610). Based on the second comparison value, the controller 210 determines whether to delete the communication link 220 and / or the BTS 206 (612). The logic flow diagram 600 then ends.

In another embodiment of the invention shown in FIG. 6, instead of the controller 210 making a subsequent decision whether to delete the reverse link, i.e., reverse link 224, without receiving a subsequent delete request, If the communication link 220 and BTS 206 are continuously considered as deletion candidates after deciding not to delete, the controller 210 may instruct the MS 202 to communicate a delete / non-delete message when the fourth time period expires (614). ). The delete / non-delete message indicates any desire of the MS to delete the communication link 220 and / or BTS 206 or not. Preferably, the controller 210 instructs the MS to send a delete / non-delete message by communicating a pilot measurement request command to the MS 202.

  In this specification, the controller 210 determines each time period of the first, second, third, and fourth time periods with the timer 215 as a reference standard. The first, second, third, and fourth time periods may each be a predetermined period or may be determined dynamically based on an algorithm. These time periods or algorithms may be stored in one or more memory devices 214.

Upon receipt of the indication, the MS 202 moves to the controller 210, which receives a delete / non-delete message from the MS indicating the desire to delete the communication link 220 and / or BTS 206 or not (616). Preferably, the deletion / non-deletion message includes a PSMM message in which the MS has embedded an indication of whether to delete or not delete the communication link and / or BTS. Deletion / non-deletion messages may be communicated to communication link 220 and / or BTS 206
The controller 210 determines 618 a second reverse link quality measure for the first reverse link 224, which is described in detail above with respect to step 608. ing. The logic flow diagram 600 then proceeds to step 610, where the controller 210 compares the second reverse link quality measure and the quality measure threshold to generate a second comparison value, and the second comparison Based on the value, it is determined whether to delete the communication link 220 and / or the BTS 206 (612). The logic flow diagram 600 then ends.

In summary, an MS such as MS 202 typically determines whether to delete a communication link such as communication link 220 and / or a BTS such as BTS 206 based on the performance of the forward link 222 associated with the communication link and BTS. Prior to deciding to delete a communication link in order to avoid deleting a communication link that has a weak forward link but a strong reverse link, the communication system 200 determines that the reverse link associated with the communication link 220 or BTS 206 to be deleted. Determine if the directional link 224 is still good. In one embodiment of the present invention, the communication system 200 determines a quality measure associated with the reverse link and is in soft handoff mode with the determined reverse link quality measure and the reverse link 224, i.e. By comparing the quality measure (one or more) associated with one or more other reverse links 234 associated with other BTS 207 in the same active set of MS 202 as BTS 206, reverse link 224 is still good. It is determined whether it is. In other embodiments of the present invention, the communication system 200 determines the quality measure associated with the reverse link and compares the determined reverse link quality measure with a threshold value to determine whether the reverse link 224 is Determine if it is still good. Based on this comparison value, the controller 210 determines whether the reverse link 224 is still a good link, or the reverse link 224 is the best link among all reverse links 224, 234 associated with the MS. It is possible to determine whether or not there is, and thereby determine whether to delete the communication link 220 and / or BTS 206 to be deleted.

In addition, the communication system 200 causes the controller 210 to re-determine whether to delete the communication link 220 and / or BTS 206, thereby rejecting it as a result of maintaining the communication link 220 that may be marginal. Prevent communication with MSs that degrade to a possible level. After deciding not to delete the communication link or BTS in response to the delete request, the communication system 200 may send the delete / non-delete message to the MS 202 on its own without receiving another delete request. By indicating, it may be re-determined whether the communication link or BTS should be deleted. In re-determining whether to delete communication link 220 and / or BTS 206, controller 210 determines that the associated reverse link 224 is based on the frame received from MS 202 via reverse link 224 following the decision not to delete. Determine if the link is still good.

  Although the invention has been particularly illustrated and described with reference to specific embodiments thereof, various modifications can be made without departing from the scope of the invention as set forth in the claims below, and Those skilled in the art will appreciate that things can be substituted for the elements. The specification and drawings are accordingly to be regarded as illustrative rather than limiting, and all such modifications and substitutions are intended to be included within the scope of the present invention.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, benefits, benefits, solutions to problems, and any element (s) that produce or make any benefit, advantage, or solution are critical, necessary, or essential in all claims Should not be construed as specific features or elements. As used herein, the term “comprising”, “comprising” or any other derivative thereof encompasses a non-exclusive inclusion, and thus a process, method, article or device including a list of elements is Is intended to include other elements not specifically listed, or other elements unique to such processes, methods, articles, or devices. In addition, the use of the terminology used to describe relationships, if any, first and second, above and below, etc. is used only to distinguish one entity or action from another entity or action, It should be understood that no actual such relationship or order is required or implied between such entities or actions.

The block diagram of the radio | wireless communications system of a prior art. 1 is a block diagram of a wireless communication system according to an embodiment of the present invention. FIG. 3 is a logic flow diagram of soft handoff performance by the communication system of FIG. 2 in accordance with an embodiment of the present invention. 3 is a logic flow diagram of the performance of soft handoff by the communication system of FIG. 2 in accordance with various embodiments of the present invention. 3 is a logic flow diagram of the performance of soft handoff by the communication system of FIG. 2 according to another embodiment of the present invention. 3 is a logic flow diagram of the performance of soft handoff by the communication system of FIG. 2 in accordance with various embodiments of the present invention.

Claims (12)

A method for performing soft handoff in a wireless communication system, comprising:
Receiving a plurality of frames from the mobile station via each of the first reverse link and the second reverse link;
Determining a first reverse link quality measure based on a plurality of frames received via the first reverse link;
Determining a second reverse link quality measure based on a plurality of frames received via the second reverse link;
Receiving a request to delete a communication link including the first reverse link;
Comparing the first reverse link quality measure and the second reverse link quality measure to generate a comparison value;
Determining whether to delete the communication link based on the comparison value in response to receiving the request;
Include methods. The method of claim 1, comprising
Determining a first reverse link quality measure includes determining a first frame quantity based on a quality index associated with a plurality of frames received over the first reverse link;
Determining a second reverse link quality metric includes determining a second frame quantity based on a quality index associated with a plurality of frames received via the second reverse link;
The step of comparing includes comparing the first quantity and the second quantity to generate a quantity difference,
The method of determining whether to delete the communication link includes determining whether to delete the communication link based on the quantity difference. The method of claim 1, comprising
The first reverse link quality measure includes a first frame quantity received in an acceptable state via the first reverse link, and the second reverse link quality measure includes the second reverse link quality measure. A second frame quantity received in an acceptable manner via the directional link,
The step of comparing includes comparing the first quantity and the second quantity to generate a quantity difference,
In determining whether to delete the communication link,
Deciding to delete the communication link if the quantity difference exceeds a threshold;
Determining to maintain the communication link if the quantity difference does not exceed the threshold;
Include methods. The method of claim 1, comprising
The first reverse link quality metric includes a first frame quantity received in error via the first reverse link;
The second reverse link quality measure includes a second frame quantity received in error via the second reverse link;
The step of comparing includes comparing the first quantity and the second quantity to generate a quantity difference,
In determining whether to delete the communication link,
Deciding to delete the communication link if the frame quantity received in error exceeds a threshold;
Determining to maintain the communication link if the frame quantity received in error is less than the threshold;
Include methods. The method of claim 1, comprising
The plurality of frames includes a first plurality of frames,
The comparison value includes a first comparison value,
The plurality of frames includes a first plurality of frames,
Determining whether to delete the communication link includes determining, based on the first comparison value, not to delete the communication link;
The method further includes:
Following the decision not to delete the communication link, receiving a second plurality of frames via each of the first reverse link and the second reverse link;
Determining a third reverse link quality measure based on the second plurality of frames received via the first reverse link;
Determining a fourth reverse link quality measure based on the second plurality of frames received via the second reverse link;
Comparing the third reverse link quality measure with the fourth reverse link quality measure to generate a second comparison value;
Following the determination to not delete the communication link, determining whether to delete the communication link based on the second comparison value without receiving a request to delete the communication link from the mobile station;
Include methods. A method for performing soft handoff in a wireless communication system, comprising:
Receiving a plurality of frames from a mobile station via a reverse link;
Determining a reverse link quality measure based on the plurality of frames;
Receiving a request to delete a communication link including the reverse link;
Comparing the reverse link quality measure with a threshold to generate a comparison value;
Determining whether to delete the communication link based on the comparison value in response to receiving the request;
Include methods. The method according to claim 6, wherein
The step of comparing the reverse link quality measure with a threshold value to generate a comparison value includes comparing the threshold value with the number of frames received in error and whether the communication link should be deleted. At the stage of judgment,
Deciding to delete the communication link if the number of erroneously received frames exceeds the threshold;
Determining to maintain the communication link if the quantity of frames received in error is less than the threshold;
Include methods. The method according to claim 6, wherein
The plurality of frames includes a first plurality of frames;
Determining whether to delete the communication link includes determining not to delete the communication link based on the comparison value;
Furthermore, the method includes:
Following the determination not to delete the communication link, receiving a second plurality of frames from the mobile station;
Receiving a quality index associated with each frame of the second plurality of frames;
Storing the received quality index associated with the second plurality of frames;
Following the determination to not delete the communication link, based on the stored quality index associated with the second plurality of frames, without receiving a request to delete the communication link from the mobile station, the communication link Determining whether or not to delete,
Include methods. A device for performing soft handoff in a wireless infrastructure,
Receiving a plurality of frames from the mobile station via each of the first reverse link and the second reverse link;
Determining a first reverse link quality measure based on a plurality of frames received via the first reverse link;
Determining a second reverse link quality measure based on a plurality of frames received via the second reverse link;
Comparing the first reverse link quality measure and the second reverse link quality measure to generate a comparison value;
Receiving a request to delete a communication link including the first reverse link;
Responsive to receiving the request to determine whether to delete the communication link based on the comparison value;
A device that contains a processor. The apparatus of claim 9, comprising:
The processor determines a first reverse link quality measure by determining a first frame quantity based on a quality index associated with a plurality of frames received over the first reverse link;
The processor determines a second reverse link quality measure by determining a second frame quantity based on a quality index associated with a plurality of frames received over the second reverse link;
The processor compares the first reverse link quality measure and the second reverse link quality measure by comparing the first quantity and the second quantity to generate a quantity difference;
The processor determines whether to delete the communication link based on the quantity difference. A device for performing soft handoff in a wireless infrastructure,
One or more memory devices;
A processor connected to the one or more memory devices,
Receiving multiple frames from the mobile station over the reverse link,
Storing a quality index associated with each frame of the plurality of frames in the one or more memory devices;
Determining a reverse link quality measure based on the stored quality index;
Comparing the reverse link quality measure with a threshold to generate a comparison value;
Receiving a request to delete a communication link including the reverse link;
Responsive to receiving the request to determine whether to delete the communication link based on the comparison value;
An apparatus including the processor. The apparatus of claim 11, comprising:
The apparatus is at least one of a base station controller, a central base station controller, and a selection / distribution unit.

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